Surgical retractors for holding tissues at the edge of a surgical incision or wound, away from the field of an operation, have been in use for many years. One style of retractor is shown in the Michelson U.S. Pat. No. 5,052,373. A first retractor arm is attached to one end of a rack and a second retractor arm is moved along the rack by rotating a gear that engages the rack teeth. Typically the second retractor arm is locked into a desired position on the rack teeth by means of a pivotally mounted pawl which is engaged in the rack teeth. The pawl is pivoted to disengage it from the rack teeth, so that rotating the gear will move the second retractor arm to a new position on the rack. With that construction, two manual operations, that is, releasing the pivoting pawl and rotating the gear, are required to change the spacing between the retractor arms. Those manual operations require two hands; and further, if the surgeon has one hand otherwise engaged in the surgical procedure, changing the position of the retractor arm requires two people. Therefore, such a construction has the disadvantage of being relatively difficult to use in the surgical situation.
Another retractor design does not include a locking pin or pawl, but instead, relies on the torquing force on the retractor arm to bind the retractor arm on the rack as the arms are spread apart. While such a design operates satisfactorily, there is always a potential that the spreading force component on the retractor arm that is in the longitudinal direction along the rack might cause the retractor arm to unpredictably slide or slip on the rack. Any unanticipated motion of a retractor arm during a surgical procedure is an obvious disadvantage of the mechanical design.
Other retractor arm designs permit the retractor arm length to be changed by sliding the retractor arm with respect to the supporting cross bar or rack. However, in those designs, it is necessary that the retractor arm be locked or latched into its new position by means of a thumb screw or other mechanism. Again, as with other manual locking devices, the process of changing the length of the retractor arm has the disadvantage of requiring several manual operations.